There is increasing demand for voice alarm systems resulting from an increased awareness on health and safety issues and legislation.
Essentially a voice alarm (VA) system is the sounder part of a fire alarm system. The two are inextricably linked and must work together. In the U.K. there are two standard codes of practice for the installation of fire alarm (FA) and voice alarm (VA) systems, these are BS 5839 pts 1 and 8 respectively.
VA systems tend to be expensive to install and they also tend to be installed by the audio industry, (public address (PA) type audio contractors). There is quite often a conflict at the interface of the two systems where the contractors and equipment meet.
Traditionally PA equipment has been build in 19″ racks from discrete parts. There has then been introduced a form of control console and interface with the FA system. Most of these systems are centralised although there are one or two so called distributed systems available. All of these systems basically work in the same manner viz;                The FA system detects a fire and gives a corresponding signal to the VA system via an interface.        This interface whilst capable of being intelligent is almost always in the form of discrete relay switches of one form or another because of the incompatibility between the two systems.        The VA system comprises a control section which then works out what this signal should be interpreted as via its programming and then routes a required pre-recorded digital message to a correct array of amplifiers.        The amplifiers then route these appropriate messages to correct sets of speakers.        The VA control system is responsible for interpreting the incoming signal and deciding the priority of the message (compared to other current audio signals) and the routing of the response through its own programming regime.        The VA control system is responsible for monitoring itself and its external wiring and giving life safety fault messages back to the FA equipment in a manner prescribed by the aforementioned standards.        
In the types of buildings that require VA systems to be installed there is also quite often a need for a PA system. Traditionally the two systems form just one (hence the involvement of the PA installation industry) where the standards dictate that the life safety function is paramount amongst other requirements. All equipment is currently made to be capable of being extended into the PA mode for example switching matrixes and paging panels are available to be connected to the equipment so that it may also be used as a PA system.
Current VA systems in their most rudimentary of forms tend to come in small racks requiring connection interfacing and programming into the FA system as a minimum. Currently the lowest available price for the smallest of such systems is well in excess of £2K.
In almost all cases where a VA system is required there will be installed an analogue addressable type of FA system. These systems have many detectors/manual call points/peripheral devices connected to one pair of wires going round a building in the form of a loop both beginning and ending at the control equipment. The devices connected to these ‘loops’ are termed analogue addressable devices since they each have an individual address and communicate continuously backwards and forwards individually with the control equipment using the pair of wires as both a power source and the data highway. One type of device that fits onto these ‘loops’ is termed an ‘output unit’ which is basically an addressable relay. One common way of triggering the VA is by an array of these output units where they are programmed in the FA control panel to give outputs at specific times under specific conditions of various detectors/manual call points being triggered.
It can be seen therefore that the interfacing of the two systems can become quite complex and that both systems require a degree of programming and interfacing. This can become quite involved and contentious when the two systems are to an extent incompatible.
It is known in the marketplace that there is a likelihood of a PA system being required as well as a VA system. However, specifications tend to be directed at providing the statutory function of VA as opposed to the utility function of PA. It is therefore not necessary to accommodate any normal PA function within the equipment, just the facility to be able to extend it to also provide this utility function at some future time and place.